The goal of the proposed research is to gain information on the physiology and biochemistry of insulin in the aqueous and vitreous of rabbits. These studies will be based upon the development of a radioimmunoassay procedure for insulin which takes into account that the physiological levels of insulin in the ocular fluids are probably substantially less than in blood. Insulin in aqueous and vitreous will be measured under a variety of conditions classically known to affect insulin levels in blood: fasting, feeding, glucose challenge, tolbutamide challenge, and alloxan diabetes. Immunoassayable insulin in aqueous and vitreous will be studied by gel filtration chromatography in order to detect different molecular-weight species related to insulin, characterize their molecular weights, and relate them to insulin and proinsulin normally found in blood. In closely related experiments, insulin receptor capacities and binding affinities of lens and cornea plasma membrane preparations will be measured using established in vitro methodology in order to characterize the interactions of insulin with these tissues. Since insulin in the ocular fluids may play a role in diabetic cataract, diabetic retinopathy, and possibly other eye diseases, basic knowledge concerning insulin in the ocular fluids, such as these investigations are designed to furnish, may lead to more effective ophthalmological management of persons afflicted with diabetes.